In some atmospheric conditions, the radius of
rotation becomes so small that the centrifugal
force becomes quite strong in comparison with
the Coriolis force. This is particularly true in low
latitudes where the Coriolis force is quite small
to begin with. In this case, the pressure gradient
force is nearly balanced by the centrifugal force
alone. When this occurs, the wind is said to be cyclostrophic. By definition, a cyclostrophic wind
exists when the pressure gradient force is balanced
by the centrifugal force alone.

This exact situation rarely exists, but is so
nearly reached in some situations that the small
Coriolis effect is neglected and the flow is said
to be cyclostrophic. Winds in a hurricane or
typhoon and the winds around a tornado are
considered cyclostrophic.

Movement of Wind Around
Anticyclones

The movement of gradient winds around
anticyclones is affected in a certain manner by the
pressure gradient force, the centrifugal force, and
the Coriolis force. The pressure gradient force acts
from high to low pressure, and the Coriolis force
acts opposite to the pressure gradient force and
at right angles to the direction of movement of
the parcel of air. The centrifugal force acts at right
angles to the path of motion and outward from
the center about which the parcel is moving. (See
fig. 3-1-12.) In the case of a high pressure center,
the pressure gradient force and the centrifugal
force balance the Coriolis force. This
phenomenon may be expressed in the following manner:

As in the case of anticyclones, gradient winds
around cyclones are affected by the pressure
gradient force, the centrifugal force, and the
Coriolis force, but the balance of the forces is
different. (See fig. 3-1-12.) In a cyclonic situation
the pressure gradient force is balanced by the Cor-iolis
force and the centrifugal force. This balance
may be expressed in the following manner:

Centrifugal force acts WITH the pressure gra-dient
force when the circulation is anticyclonic and
AGAINST the pressure gradient force when the
circulation is cyclonic. Therefore, wind velocity
is greater in an anticyclone than in a cyclone of
the same isobaric spacing.

Variations

It has been determined that, given the same density, pressure gradient, and
latitude, the wind
is weaker around a low-pressure cell than a high-pressure
cell. This is also true for gradient and